1. Field of the Invention
The present invention relates to a diaphragm of an electroacoustic transducer and a method of manufacturing thereof, and more particularly, to materials for a diaphragm of a speaker having superior characteristics with highly balanced internal loss, density and rigidity, and a method of manufacturing the diaphragm.
Conventionally, many materials have been developed for the diaphragm of the speaker in order to improve acoustic characteristics of the speaker. The diaphragm of the speaker having ideal characteristics requires low density, high rigidity, large internal loss and the like. Therefore, materials which includes a high rigidity substance such as carbon fiber and aramid fiber, or materials having a large internal loss such as polypropylene have been utilized.
In manufacturing the diaphragm, however, if the rigidity increases, the internal loss tends to be reduced, while the rigidity and the density tend to be reduced if the internal loss increases. Thus, an important object of manufacturing the diaphragm is to set the above three factors, i.e., the density, the rigidity and the internal loss of materials of the diaphragm to the best balanced state.
The characteristics of the materials of the diaphragm of the speaker which have been utilized conventionally are described, for example, in Radio Technology, August, 1983, pp. 77. More particularly, as for the diaphragm made of an aluminum alloy, for example, its density is 2.7 g/cm.sup.3, Young's modulus is 62.times.10.sup.10 dyne/cm.sup.2, and its internal loss is about 0.002. As for the diaphragm made of polypropylene, its density is 0.91 g/cm.sup.3, Young's modulus is 1.08.times.10.sup.10 dyne/cm.sup.2, and its internal loss is 0.07. Meanwhile, as for the diaphragm for a general speaker made of wood pulp, its density is 0.55 g/cm.sup.3, Young's modulus is 1.32.times.10.sup.10 dyne/cm.sup.2, and internal loss is about 0.05.
As described above, the diaphragm made of wood pulp has an appropriately large internal loss and a low density compared with the diaphragm made of an aluminum alloy: however, it has a disadvantage of narrower frequency band due to an insufficient rigidity.